The present invention relates to a control system for a vane type variable displacement pump.
The prior art contains a control device for a vane type variable displacement pump, such as that shown in FIG. 1. A cam ring 1 of a vane type pump is pivotally mounted at a protrusion thereof to a support member of the pump by a pin 2, which serves as a fulcrum. Provided radially inward of the cam ring 1 is a rotor 4 having a plurality of vanes 3 which are slidable through the rotor 4 in a radial direction. The opposed faces of each pair of adjacent vanes 3 define, along the arc of the radial outward surface of the rotor 4 and the interior surface of cam ring 1 which the pair of vanes intersect, chambers which rotate and change in volume depending on angular position. The cam ring 1 is arranged in a variable eccentric relationship with the rotor 4. The cam ring 1 also has a lever 1a which is integrally formed on and extends from the cam ring 1 to receive a force due to a spring 5 and a force due to a piston rod 6a of a hydraulic cylinder 6 acting oppositely on the lever 1 a, so that the balance of both forces determines the amount of eccentricity of the cam ring. In FIG. 1, the rotor 4 rotates in a clockwise direction, so that hydraulic fluid is drawn from a reservoir 7 by a suction port 1b through an oil line 8, and the pressurized hydraulic fluid is delivered from a delivery port 1c to an oil line 9. The pressurized hydraulic fluid at the oil line 9 is regulated to a predetermined pressure (line pressure) by a control valve 10, and is delivered to hydraulic equipment, such as a clutch, which is not shown. The oil line 9 is also leads to a regulator valve 11. The regulator valve 11 acts to apply the line pressure to a hydraulic cylinder 6 through an oil line 12 when the line pressure in the oil line 9 is higher than a preset pressure, and to exhaust the hydraulic fluid from the hydraulic cylinder 6 to the reservoir 7 when the line pressure is below the preset pressure. With such a construction, when a rotating speed of the rotor 4 is low, substantially no hydraulic pressure is supplied to the hydraulic cylinder 6 so that the bias force of the spring 5 encounters substantially no resistance from the piston rod 6a and the amount of the eccentricity becomes maximum, whereas when the rotating speed of the rotor is high, the line pressure is supplied to the hydraulic cylinder 6 and the amount of the eccentricity becomes small. In this manner the amount of delivery at a low rotating speed can be assured while energy loss at a high rotating speed can be reduced.
However, in a control device for such a prior art vane type variable displacement pump as described above, problems exist such as follows. Namely, since a hydraulic cylinder has to be used to control the amount of the eccentricity of the cam ring in the control device, a large number of parts are required, and thus its cost becomes high and moreover, a large space is required.